Apparatus for the preparation of semiconductor material



1956 H. R. BARKEMEYER ETAL 3,231,337

APPARATUS FOR THE PREPARATION OF SEMICONDUCTOR MATERIAL Filed Oct. 29,1963 INVENTORS HENRY R. BARKEMEYER WILLIAM J. McALEER BY PET R |.POLLAATTORNEY 3,231,337 APPARATUS FGR THE PREHARATIOIJ 9F SEMICONDUCTORMATERIAL Heriry R. Barkemeyer, Ncrth Plaintield, William J.

McAleer, Old Bridge, and Peter I. Pollahscotch' Plains,

NJ., assignors tdMerckdz Co., Inc, Rahway, Ni, a

corporation of New Jersey Filed Oct. 29, 195$,S6E. No. 319,766 2 Claims.(Cl. 23-277) This invention relates to growth of semiconductor materialfrom the vapor phase and more particularly, to an apparatus for makingbulk semiconductor material in a continuous manner.

It is known in the art to prepare semiconductor materials by vapordeposition upon a starting element, or substrate, which is heated to atemperature at which deposition can occur thereon. For example, GroupHIV semiconductor compounds are prepared by a batch process from thevapor phase involving a disproportionation reaction whichtransfersmaterial from a hot to a cold zone,

the thermal gradient being provided by a furnace.

Accordingly, it is an object of the present invention to provide anapparatus for growing bulk semiconductor material from the vapor phase.

Another object of this invention is to provide bulk semiconductormaterial by a continuous, open tube process.

A further object of the instant invention is to provide Group Ill-Vsemiconductor rods in a continuous manner by growth from the vaporphase.

A feature of the present invention is the provision of a retractablecold pedestal having a semiconductor seed member thereon for growingelongated, bulk semiconductor-material from the vapor phase in acontinuous manner.

Another feature of this invention is the provision of a continuous feedsystem for supplying metallic reactant material in the preparation ofGroup HIV semiconductor material by growth from the vapor phase.

Still another feature is the provision of a withdrawal mechanism forgrowing bulk semiconductor material in a continuous manner.

These and other objects will be made apparent from the following moredetailed description of the invention, in which reference will be madeto the accompanying drawing, in which:

The figure is a schematic illustration of the apparatus of the presentinvention.

In accordance with the present invention, there is provided an apparatusfor making bulk semiconductor Group HIV compounds of the generalformula:

where A and B are different elements but both of Group III, i.e., boron,aluminum, gallium or indium, and C and D are different elements but bothof Group V, i.e., nitrogen, phosphorus, arsenic or antimony; wheresubscripts x and y denote atom proportions whose values can change fromzero to unity, inclusive, in a continuous and controlled manner.

Referring now to the figure, there is shown schematically the apparatusfor forming bulk semiconductor material according to the presentinvention. The apparatus includes reaction chamber 1 which is formed ofa suitable material, such as quartz, and is in the form of an open tubehaving an inlet 2 and an outlet 3. Surrounding the tube is a furnace 4which may be used to preset the temperature within the reaction chamberin a given manner. For example, the furnace may be maintained at anelevated temperature so that the reactants are in the vapor state. Thefurnace may conveniently comprise an elec- United States Patent3,231,337 Patented Jar-1.25, 1966 "ice trical insulating ceramic shellsuch as Alundum in which are embedded resistance heating wires, spirallywound, all forming a cylindrical heating device within which thereaction chamber may be positioned. The resistance heating wire of thefurnace may be connect-ed to a source of electrical energy through eachof the furnaces individual terminal wires.

For purposes of clarity only, and not as a limitation thereof, thefollowing description of the present invention will be described withparticular reference to the formation of gallium phosphide material.

Into the reaction chamber 1 is introduced an elemental or metallicconstituent of the semiconductor, illustrated as 5, contained'within aboat 6, suitably one made of vitreous carbon material; the material maybe continuously fed into the chamber from reservoir 7.

A supply line, generally indicated as 8, is provided at the inlet part 2of the open tube vessel for admission of gaseous reactants into thereaction chamber. For example, if it is desired to form bulk galliumphosphide material, themetallic constituent 5 is gallium. Aphosphorushalide, illustrated as"9,such as phosphorus trichloride, serves as atransport agent for the non-metallic constituent. The transfer agent isadmitted into the reaction chamber in a stream of H With in the reactionfurnace is placed a suppoit'element It Positioned on the support is asingle crystal semiconductor starting or seed member 11. As shown in thefigure, the support is in the form of a pedestal. Within the pedestalelement is a duct 12 for admitting a cooling gas 13, such as nitrogen,therethrough. As the cooling gas leaves exit nozzle 14 of duct 12, itcirculates around and cools seed 11 to a low temperature. The gases arecontinuously circulated around the pedestal element in the directionindicated by arrow 15.

Cooling of the seed in the manner-described above provides a cold sitewithin the reaction chamber at which formation of gallium phosphide mayoccur by disproportionation of the intermediate reactive speciesthereof.

The layer which forms on the single crystal substrate member by thistechnique is an epitaxial crystal. When the substrate semiconductormaterial is the same as the material being deposited from the vaporphase, the epitaxial layer has the same chemical constitution as thesubstrate but may differ in conductivity type or degree as desired. Onthe other hand, when the substrate and vapor materials are differentchemically, then the first epitaxial layers are generally a solidsolution of the substrate and vapor depositing materials, while the restof the rod is of the latter only.

Generally the pedestal is maintained at a temperature of between 8G09()0C. for the preparation of Group III-V semiconductor material. Preferablyit is at 850 when gallium phosphide material is produced.

As the deposited material increases in length, a bulk rod is obtained.As the rod is extended, it is necessary to retract the pedestal at arate approximately equal to the rate of growth of the rod so that anelongated rod can be produced with a smaller reaction vessel. AsWithdrawal mechanism 16 is provided for the purpose of pulling thepedestal downward in the direction of arrow 17. Generally the pedestalis retracted at a rate of about 10 mils per hour. There is thus providedan elongated bulk rod of single crystal semiconductor material.

Example 1 Using the apparatus of the figure, high purity gallium metalof semiconductor grade is charged in a vitreous carbon boat and insertedin a 1'' OD. quartz tube, which, in turn, is inserted in an 18" globarfurnace preset at about 1000 C. The quartz tube then is connected to agas entrance line and a gas exit line. Hydrogen then is passed throughthe system at 170 ml./min. for two hours in order to remove moisture andoxide films on the molten gallium. A flask which is charged with 5 l. ofreagent grade phosphorus trichloride is immersed in ice water at C. Thehydrogen gas is passed through the phosphorus trichloride at 70 ml./min.for an extended length of time. The vapor pressure of phosphorustrichloride at 0 C. is 35 mm. The seed member is single crystal galliumphosphide. Gaseous nitrogen gas is continuousy circulated at a flow rateof l./rnin. in the predestal member to maintain the substrate of about850 C. At the end of the run there is observed a built-up rod of galliumphosphide on the gallium phosphide seed. The gas input feed is thenswitched to helium and the tube is cleaned of excess phosphorustrichloride and gallium chloride which are formed during the reaction.The withdrawal mechanism retracts at a rate of mils per hour. At theconclusion of the run, the tube is opened while excluding air, cooled toroom temperature, and the elongated gallium phosphide rod is removed.

Example 2 The procedure of Example 1 is followed using indium metal inplace of gallium metal and an indium phosphide seed at 800 C. in placeof a gallium phosphide seed to produce an elongated rod of indiumphosphide.

Example 3 The procedure of Example 1 is followed using arsenictrichloride in place of phosphorus trichloride to produce an elongatedrod of gallium arsenide.

While the invention has been described with reference to certainpreferred embodiments thereof, it will be understood that changes andmodifications may be made which are within the skill of the art.

What is claimed is:

1. Apparatus for the formation of bulk semiconductor material of thegeneral formula:

(A B )III (C D )V where A and B are different elements but both of GroupIII and C and D are different elements but both of Group V and wheresubscripts x and y denote atom proportions whose values are zero tounity, inclusive, which comprises:

(a) an open reaction chamber,

(b) a boat within said chamber,

(c) means for continuous charging of said boat with the metallic elementof the specific material to be formed,

((1) means for heating said metallic element to a predeterminedtemperature adequate to transform said element to the vapor phase, p

(e) a transport gas for said non-metallic element,

(1') a pedestal support element Within said chamber for supporting awafer,

(g) cooling means positioned in said support for cooling said wafer to atemperature in the range 8005-900 C. where deposition can occur thereon,and

(h) withdrawal means associated with said pedestal for retracting thesame at about the same rate as that at which Group III-V material isbuilt-up on said seed.

2. Apparatus for the formation of gallium phosphide,

which comprises:

(a) an open reaction chamber containing a boat adapted to be chargedwith gallium metal,

(b) means for continuously charging said boat with gallium metal,

(c) a furnace for heating said gallium to above 1000" C.

to transform said gallium to the vapor phase,

(d) a phosphorus trichloride tranpsort agent for said non-metallicelement,

(e) a pedestal within said chamber,

(f) a single crystal gallium phosphide seed member positioned on saidsupport, 1 (g) nitrogen cooling gas circulating within said pedestal forcooling said seed to a temperature of about 850 C. where deposition canoccur thereon, and

(h) withdrawal means for retracting said pedestal at a rate of about 10mils per hour.

References Cited by the Examiner UNITED STATES PATENTS 4/1958 Gastinger1l7-107.2-X 6/ 1963 Wegcner 23277

1. APPARATUS FOR THE FORMATION OF BULK SEMICONDUCTOR MATERIAL OF THEGENERAL FORMULA: